Bears nurse their young, a central aspect of parental care. This practice is central to the survival and development of bear cubs, laying the groundwork for their growth, immunity, and eventual independence. The nursing period is a time of rapid transformation and learning, shaped by the mother’s care and her milk’s unique properties.
The Act of Nursing
Bear cubs are typically born in the den during winter, often in January or February, while the mother hibernates. At birth, cubs are small, weighing between 8 to 16 ounces, blind, and covered in sparse fur. Despite the mother’s reduced metabolic state during hibernation, she awakens to give birth and nurses her offspring.
Nursing continues within the den for several months, with cubs frequently suckling from their mother’s six nipples. This period is important for their growth and development before they emerge from the den in spring. While some milk is consumed during denning, milk production increases significantly, by as much as four-fold, once the family emerges. Depending on the species, the nursing period varies; black bear cubs are typically nursed for about 1.5 years, while polar bear cubs may nurse for 2.5 to 3 years.
Nurturing Cub Growth and Survival
Bear milk is rich, a concentrated source of nutrients for rapid cub growth and development. Its fat content is high, ranging from 20 to 25 percent, far surpassing that of human or cow milk. This high fat concentration provides substantial energy for cubs to build fat reserves and maintain body warmth, especially in the cold den.
Beyond fats, bear milk also contains protein and antibodies. These components support muscle and tissue development and strengthen the cubs’ developing immune systems, protecting them from various diseases. The milk enables cubs to gain weight rapidly; for instance, a black bear cub born at less than a pound can grow to about six pounds by the time it emerges from the den. This rapid growth is important for their survival in the outside world. The mother’s body condition, particularly her fat reserves before hibernation, directly influences the growth rate of her cubs, with fatter mothers producing cubs that grow faster and are larger upon den emergence.
Transition to Self-Sufficiency
Following intense nursing, bear cubs gradually transition from an exclusively milk-based diet to solid foods. This weaning process typically begins around five to eight months of age, though cubs continue to nurse while experimenting with other food sources. Even after weaning, cubs remain with their mother for an extended period to learn survival skills.
The mother bear plays an important role in educating her offspring, demonstrating how to forage for food, identify safe plants, berries, and insects, and, for some species, how to hunt. She also teaches them how to navigate their environment, climb trees to escape danger, and recognize potential threats. This extended family period, which can last for 17 months for black bears and up to 2.5 to 3 years for grizzly and polar bears, allows cubs to master these behaviors. The bond between mother and cubs remains strong until the mother is ready to mate again, at which point she encourages her now-independent offspring to disperse and establish their own territories.